- Following are certain statements regarding gibberellic acid (GA) signal transduction:
(A) DELLA proteins negatively regulate GA signalling.
(B) Degradation of GA receptor (GID1) is mediated by DELLA proteins.
(C) Ubiquitination and subsequent degradation of DELLA proteins are independent of GID1.
(D) GA binding to GID1 promotes binding of GID1 to DELLA proteins.
Which one of the following combination of statements is correct?
(1) A and B (2) B and C
(3) C and D (4) A and D
Correct answer: (4) A and D
Explanation:
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(A) DELLA proteins are negative regulators of gibberellin (GA) signaling, functioning as repressors that inhibit GA responses in plants. This is true.
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(B) There is no evidence that DELLA proteins mediate degradation of the GA receptor (GID1). Instead, GID1 acts as the GA receptor that binds GA and DELLA. So, B is false.
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(C) Ubiquitination and degradation of DELLA proteins is dependent on GID1 binding. GA binding to GID1 promotes interaction with DELLA, leading to DELLA ubiquitination and degradation. Hence, C is false.
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(D) GA binding to GID1 promotes the binding of GID1 to DELLA proteins, facilitating their ubiquitination and degradation, thus derepressing GA responses. This is true.
Option-wise:
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(1) A and B — B false.
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(2) B and C — both false.
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(3) C and D — C false.
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(4) A and D — correct.
Gibberellin signaling is tightly controlled by the interaction between the GA receptor GID1 and DELLA proteins, with GA binding enabling GID1 to target DELLA repressors for degradation, thereby activating GA-responsive gene expression and promoting plant growth.
